1. Field of the Invention
The present invention relates to splitters that use elastic waves such as surface acoustic waves, boundary acoustic waves or bulk elastic waves, and in particular relates to elastic wave splitters that include a transmission filter and a reception filter defined by elastic wave filters.
2. Description of the Related Art
In recent years, splitters using elastic wave resonator filters have been widely used as splitters in communication devices. Examples of such an elastic wave resonator include a bulk elastic wave resonator filter, a surface acoustic wave resonator filter and a boundary acoustic wave resonator filter.
In such elastic wave resonator filters, intermodulation distortion (IMD) is generated due to the nonlinearity of the filters. In addition, degradation of filter characteristics is a problem.
In Japanese Unexamined Patent Application Publication No. 2010-21914, a splitter is disclosed having a configuration in which generation of intermodulation distortion is suppressed. FIG. 15 is a circuit diagram of the splitter described in Japanese Unexamined Patent Application Publication No. 2010-21914.
An antenna terminal 1003 of a splitter 1001 is connected to an antenna 1002. A transmission filter 1004 and a reception filter 1005 are connected to the antenna terminal 1003. The transmission filter 1004 is a ladder filter composed of a plurality of BAW resonators. In addition, the reception filter 1005 is a balanced filter. An input terminal 1005a of the reception filter 1005 is connected to the antenna terminal 1003 and output terminals of the reception filter 1005 are a pair of balanced reception terminals 1005b and 1005c. A first longitudinally-coupled-type SAW resonator filter 1006 is connected between the input terminal 1005a and the reception terminal 1005b, and a second longitudinally-coupled-type SAW resonator filter 1007 is connected between the input terminal 1005a and the reception terminal 1005c. 
In order to achieve impedance matching between the reception filter 1005 and the transmission filter 1004, an inductance L1 is connected between the antenna terminal 1003 and a ground potential and an inductance L2 is connected between the antenna terminal 1003 and the transmission filter 1004. In addition, in the transmission filter 1004, first and second resonators 1011 and 1012, which are serially divided into two, are connected in series with each other on the antenna terminal side. In addition, in the reception filter 1005, SAW resonators 1021 and 1022 and SAW resonators 1031 and 1032, which are serially divided into two, are arranged on the input terminal 1005a side. That is, in each of the transmission filter 1004 and the reception filter 1005, the resonator on the antenna terminal side is composed of two resonators, which are connected in series with each other. In such a case, the area of the resonator is increased approximately fourfold, as a result of the resonator being serially divided into two, without the impedance of the resonator changing. Consequently, the power density per unit area is reduced to ¼ and non-linear distortion of the resonator can be reduced. Therefore, intermodulation distortion in the splitter can be suppressed.
However, in the splitter 1001 described in Japanese Unexamined Patent Application Publication No. 2010-21914, the areas of the resonators are increased and therefore it is difficult to reduce the size of the splitter 1001. In addition, resistive loss is increased and therefore, there has been a problem in that insertion loss is increased.